When image sensing is performed on a person with an image sensing apparatus such as a digital camera, image sensing at well focus on the person's face as a subject and with optimum exposure for the face is required. In conventional cameras, a particular area is selected from predetermined plural areas in a screen, based on information on distance to a subject, subject contrast information or information in a user's visual axis, then image sensing is performed with focus on the particular area and optimum exposure for the particular area.
However, in the above method, if the person's face as a subject is not included in the predetermined plural areas, correct exposure and focus cannot be obtained on the person's face.
Accordingly, a camera having a function of detecting an area corresponding to a human face from an image by image processing has been proposed in Japanese Patent Application Laid-Open No. 2001-215403. According to this camera, image sensing can be performed with well focus on a human face in any position of an image sensing screen and with optimum exposure for the human face.
Further, as a method for detecting an area corresponding to a human face from an image by image processing, Japanese Patent Application Laid-Open No. Hei 8-63597 discloses detection of face candidate area presumed to be a face from an image, matching between the face candidate area and predetermined face reference data, and determination as to whether or not the face candidate area corresponds to the human face based on the result of matching.
According to the method proposed in Japanese Patent Application Laid-Open No. Hei 8-63597, the inclination of face in the image signal upon image sensing with the camera in a vertical position is different from that upon image sensing with the camera in a lateral position, as shown in FIG. 8. Accordingly, the face area detection processing must be performed plural times in different directions.
To detect a human face with high precision from an image obtained by a camera and reflect the result of detection in image sensing conditions, time for face detection must be reduced as much as possible. If much time is taken in face detection, processing time for control of focusing on the face and exposure is delayed, and release time lag from the user's image sensing instruction to actual image sensing with the camera is increased.
Accordingly, there is room for improvement in high speed detection of human face from an image obtained by image sensing.